1. Field of the Invention
The present invention relates to a memory card, and more particularly, to a memory card with electrostatic discharge protection.
2. Description of Related Art
An electronic product operating in an actual working environment often encounters the destructive impact of electrostatic discharge (ESD). If a suitable form of protection is not set up, devices within the electronic product may cause permanent damages. In general, the ESD voltage is substantially greater than the power source voltage for operating the electronic product. When an ESD occurs, the ESD current is likely to burn up the internal devices. Therefore, isolating the ESD current to prevent possible damage to the devices is very important.
To prevent the aforementioned ESD phenomenon, some ESD protection facilities are set up inside the electronic products. For example, grounding fingers of U.S. Pat. No. 5,319,523 can be electrically connected first to back plane circuit board than signal fingers by position arranging of grounding fingers and signal fingers on card edge connector portion of printed circuit board when the card edge connector portion of the printed circuit board is inserted into the a connector. The U.S. Pat. No. 5,319,523 does not teach that conductive surface traces 66, which electrically connect the grounding pad and grounding finger, (ESD protection path) extend to the edge of the circuit board, and therefore electrostatic charges cannot be collected by the ESD protection path and rapidly transmitted out of circuit board through the ground pad and fingers. Furthermore, the U.S. Pat. No. 5,319,523 does not teach the technique that can prevent electrostatic charges entering the conductive surface traces 56 (signal path) from damaging the components on the printed circuit board. Similarly, U.S. Pat. No. 6,804,119 does not teach the techniques that ESD protection path extend to the edge of the circuit board and prevent electrostatic charges from entering signal path.
The convention memory card utilizes its casing to protect the internal devices and provides a certain degree of ESD shielding capacity. However, as the memory card evolves toward smaller dimension according to the current trend, the casing alone can hardly provide sufficient ESD protective capacity.
FIG. 1A is a diagram showing the layout of the printed circuit board of a conventional memory card. As shown in FIG. 1A, a patterned circuit layout is disposed on the printed circuit board 100. Because the process of fabricating the printed circuit board 100 requires a plating treatment, each electrical path in the printed circuit board 100 is extended into areas outside the cutting lines 110 to facilitate the plating operation. The extended electrical paths disposed to facilitate the plating operation are called plating lines. After completing the processes (for example, the plating operation) for forming the printed circuit board 100, the board is cut out along the cutting lines 110. FIG. 1B is a diagram showing the printed circuit board 100 of a conventional memory card after completing the board cutting process.
As shown in FIG. 1B, after the board cutting process, subsequent production processes including disposing and soldering memory devices (such as flash memory integrated circuits) and other devices, assembling the casing and so on are performed on the printed circuit board 100 to produce a complete memory card. Because the plating lines for facilitating the plating operation cross over the cutting lines 110, the plating lines at the edge of the printed circuit board 100 will be exposed after the cutting operation. Since each of these plating lines is electrically connected to the corresponding electrical path in the printed circuit board 100, static electric charges will flow into the electrical paths through the plating lines at the cut edges of the printed circuit board 100 when an ESD occurs. Ultimately, the devices (not shown) on the printed circuit board 100 may be damaged.